Cao 曹 was a rather unimportant mid-sized feudal state of the Zhou period 周 (11th cent.-221 BCE) with an unspectacular history (at least as far as historiography informs us). The first ruler of Cao was Cao Shu Zhenduo 曹叔振鐸, a brother of King Wu of Zhou 周武王. Earl You 曹幽伯 (r. 834-826) was killed by his younger brother, Earl Dai 曹戴伯 (r. 825-796). During the reign of Duke Gong 曹共公 (r. 652-618), Prince Chong'er 重耳 of Jin 晉 stayed in Cao and was not treated with the necessary respect. When he became duke of Jin (Duke Wen 晉文公, r. 636-628), he took revenge and attacked Cao. Duke Gong of Cao was captured and only released after a while.
Duke Cheng 曹成公 (r. 577-555) met the same fate and was taken prisoner by Jin for a while. Duke Dao 曹悼公 (r. 523-515) was taken prisoner by the state of Song 宋. When he was absent, his brother, Prince Ye 野, was enthroned as Duke Sheng 曹聲公 (r. 515-512). Duke Gong died in Song, but his corpse was transferred to Cao to be buried. Duke Sheng was assassinated by his uncle, who mounted the throne as Duke Yin 曹隱公 (r. 511-506). Duke Yin himself was killed by a brother of Duke Sheng, Duke Jing 曹靖公 (r. 505-502). These fratricidal phase was ended with Duke Jing's son, Prince Yang 陽, who was also the last ruler of Cao, known as Earl Yang 曹伯陽 (r. 501-487). The history of Cao ends with a dream, in which only a certain Gongsun Qiang 公孫彊 would be able to save the state. Gongsun Qiang was a hunter, and because of the dream, he stood in high favour of Earl Yang. He suggested to the duke to become a hegemonial lord (ba 霸), and in the belief to be on the safer side, the Earl offended the ruler of Song and ignored to pay reverence to Jin. When the army of Song attacked, the duke of Jin refused to help Cao. The Earl and Gongsun Qiang were executed, and the dynasty was ended. Cao became part of Song.

Source: Shiji 史記 35, Guan Cai [Cao] shijia 管蔡世家.

Rulers of Cao 曹Capital: Taoqiu 陶丘 (modern Dingtao 定陶, Shandong)Note: The reign dates are given according to Western reckoning. In Chinese chronicles, the year after the first New Year of a rule is seen as the first year of reign. Example: Duke Zhao died in 653, his son Duke Gong immediately acceeded to the throne, yet Chinese chronicles see 652 as his first (full) year of reign (Cao Gongong 1).